1. Field of the Invention
The present invention relates generally to navigation systems for unmanned vehicles, and more particularly is a high-resolution system that typically will be utilized in inertial navigation systems (INS) for land vehicles. The system of the present invention uses radio frequency (RF) tags or xe2x80x9cbeaconsxe2x80x9d placed by a manned path marking vehicle to define a route that is to be traversed by manned or unmanned follower vehicles.
2. Description of the Prior Art
Military operations often include a mission requirement of resupplying forward units using both manned and unmanned ground vehicles. However, there currently does not exist an acceptable high-speed, precision robotic path following solution for on-road and off-road operations.
Current robotic vehicle solutions that rely on autonomous mobility sensors and software are limited by the speed at which the sensors and software can detect and interpret terrain features and landmarks. Moreover, this approach does not work in complex environmental conditions, i.e., poor lighting conditions, haze, smoke, rain, etc. Further, although high-accuracy INS is readily available for ground vehicles, the INS error increases without bound as a function of distance traveled. Attempting to correct the INS error using a GPS reference is only accurate to xc2x110 m, which is inadequate for land navigation of a robotic vehicle.
Current art systems utilizing differential or relative GPS systems offer accuracies of xc2x10.2 m to xc2x11 m, and carrier phase GPS can provide position accurate to xc2x12 cm; however, both these types of systems are vulnerable to jamming. Moreover, these systems require line-of-sight RF communications between the differential or relative station and the navigating vehicle. Further, neither differential nor relative GPS navigation-based solutions can satisfy scenarios involving large separations in time and distance between the leader and follower vehicles. The current art approaches require the leader vehicle to be on the path when followers are performing their missions, which is an unnecessary risk to the human crew and adds cost to the operation.
Accordingly, it is an object of the present invention to provide a path following system that does not require the path marking vehicle to be close in time or space to the follower vehicles.
It is a further object of the present invention to provide a path following system that utilizes marking beacons with signals that are not easily jammed.
It is a still further object of the present invention to provide a path following system that functions well in poor visibility conditions.
It is a still further object of the present invention to provide a path following system that provides high speed position determination with a high degree of accuracy.
The present invention is a high-resolution path marking system utilized with inertial navigation systems for land vehicles. The system of the present invention uses radio frequency tags or xe2x80x9cbeaconsxe2x80x9d to mark a route to be traversed by manned or unmanned follower vehicles. The RF tags serve as references to correct time and distance traveled dependent errors that accumulate in the follower vehicle""s inertial navigation system. The position of each tag is accurately encoded into its memory using a manned path marking vehicle that xe2x80x9cproofsxe2x80x9d the route in advance of the follower vehicles. Since the inertial navigation system for the path marking vehicle and for the follower vehicles are synchronized at the start of the route, any errors accumulated in the followers"" INS with respect to the path marking vehicle are eliminated at the prescribed intervals where the RF tags are placed.
The RF tag solution embodied by the present invention offers a superior, low-cost approach to the problem of path marking for manned and unmanned follower vehicles. In the approach herein, the manned path marking vehicle can lay the route days, weeks, or even months in advance. Once the path is marked, it can be reused many times by the follower vehicles without further human intervention. Further, the short-range, ground based RF tags used in this method are less susceptible to jamming, and the tags are covert, i.e. the tags are small and transmit only when interrogated by a secure query signal.
Some of the advantages of the system of the present invention relative to the prior art are as follows:
1. Low complexity
Operates without the need of a Global Positioning Satellite (GPS) signal
Does not require expensive machine vision sensors to detect obstacles
2. Low cost (RF tags cost only a few dollars each)
3. Secure (RF tags radiate only after being interrogated by a coded query signal)
4. Covert
RF tags are very small and can be easily disguised to match terrain features, e.g., small stones, twigs, brush, leaves
Vehicle to vehicle communications are not required to navigate a path
5. Reusable (once laid, the path can be used many times by the followers without further human intervention)
6. Low susceptibility to jamming (the tags are short-range and use ground-based RF)
7. Works in complex and cluttered terrain environments